Technical Abstract:
During latency, pseudorabies virus (PRV) DNA is preferentially retained in the neurons of the trigeminal ganglion and a spliced 8.5 kilobase poly-A RNA, designated large latency transcript (LLT), is transcribed. Organization of the PRV LLT/UL1-3.5 promoter is quite complex. There are two TATA boxes in this region. LLT is transcribed in the rightward direction while the UL1-3.5 gene cluster is transcribed in the leftward orientation. In this work, we studied the activities of the LLT promoter and the UL1-3.5 gene cluster promoter by transient expression reporter gene assay in cells of neuronal and non-neuronal origins. Specifically, we examined the promoter activities of the first TATA box with its 5' sequence (LAP1) and the second TATA box with its 5' sequence (LAP2). The UL1-3.5 promoter driven constructs gave no reporter gene activity in any of the experiments. Reporter gene activity was detected with LAP2 gene constructs in both neuronal and non-neuronal cells, but not with LAP1 constructs. This is surprising because transcription of PRV LLT in vivo has been attributed to LAP1 and the initiation site was mapped downstream of the LAP1 TATA box. Although the promoter activity of LAP1 alone was nil to negligible, there was a 3- to 10-fold enhancement of reporter gene activity if LAP1 and LAP2 were aligned in tandem when compared to the activity from LAP2 alone.